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Edited Date/Time
2/20/2015 2:42pm
Have any of you guys owned or ridden a 250F in which an Athena oversized kit was installed? I just wanted to hear what some of you may have to say about it , and what the overall experience of it was.
Besides buying the kit........what else is there to do? How do they work with EFI....as in do you need to some how reprogram the EFI unit , electrical issues , shit not fitting right , ect?
I'd also be curious to find out what a person may have to do to the head and exhaust. Will an after market exhaust made for a 250cc motor work well on a 290cc motor? And the dome of the head.....does this need to be milled in any way?
Thanks in advance dudes.
Besides buying the kit........what else is there to do? How do they work with EFI....as in do you need to some how reprogram the EFI unit , electrical issues , shit not fitting right , ect?
I'd also be curious to find out what a person may have to do to the head and exhaust. Will an after market exhaust made for a 250cc motor work well on a 290cc motor? And the dome of the head.....does this need to be milled in any way?
Thanks in advance dudes.
Slip......if you see this thread please chime in. Love to hear your thoughts on this.
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If I did another one, I would strongly consider doing a new Honda as they apparently love a bit more displacement, at the same size.
Bents....what made you choose the " Cylinder works " over the Athena kit? They look real similar as far as what comes in the kit. I'm leaning towards picking up a newer Suzuki RMZ 250 as I really like the way the bike feels , especially in the cornering dept.
I dunno....my way of thinking is having something in between a 450 and a 250 in the power dept and keeping the bike light like a 250 is / would be a good Vet machine. And again....I love my 450 , but I'm tired of making mistakes on that beast when I get tired....because the SOB makes me pay for it. I need something lighter , slower , updated suspension.....and something that won't destroy me with a little whiskey throttle if it happens. That 450 has no forgiveness in it.
Dirt Rider 270cc shootout
07: I did this one first, Athen 280 with a TMR race team head, the full deal ported w/ xeledyne valves a custom cam, tokyo mods modded carb, and a white bros single lowboy carbon pipe and the head was milled a little because the compression was unreal! now this bike was AMAZING!!!!!!! Once we got the jetting right this bike was exactly the kind of I had dreamed of. I HATED my 450's and at the time was about 220lbs so a 250f just wasnt enough. Now I never dyno'd the bike but it made insane HP for a 250f and yes it was all 250f in every aspect but the motor, this bike was a rocket! I had no problem hanging with 450's and didnt lose any revs at all only it did rev a tick slower but wasnt that bad it hauled ass! It was easily as powerful as the yz400f maybe more....I loved that bike and the trick is to get a top end only cam for a big bore since the bigger piston brings the power lower it spread the power perfectly I was even able to run a 13/48 without a problem.....Like I said I loved that bike until the day it gave me the infamous Honda-bog at the face of a peak to peak 60' double and I ended up with 3 broken vertebrae (lost feeling below my waist for 5-10mins it was SCARY) a broken sternum dislocated shoulder and some internal bleeding. Took me almost 2 years to get back on a bike and I was over 4 strokes so i got a couple RM250's and never looked back.
04: This one had a bad head and I had a spare 07 head from the bike above, so I used my 07 head with a stage 2 hotcam (top end) an FMF pipe, 13/48 gearing and rode this one out on the hills and desert. It was so much fun to ride this bike as well although it didnt have the same brute power the 07 had it was similar running to a standard 250f but with more stones. I really liked this bike too with this setup and both got stiffer clutch springs ...... I only got to ride the 04 like 3 times because of the injury stated above but it was a brilliant bike in the desert and hills and was never at a loss for power. i ended up selling them both due to injury and got the RM's .....a decision Ill never regret but yes if I had to switch back I would most definitely run a 280/290cc kit on ANY 250f
Those Athena big bore kits if done right are worth their weight in GOLD as far as Im concerned. They were very rideable and I never had a problem with either (except for that 1 time bog) and because of that I was finished riding 4 strokes these big bore bikes were as close to riding a 250 2 stroke as I could get but once I got back on the smokers I realized they are flat out better bikes for me. IMO definitely get the Athena big bore kits they are less than the cost of a OEM top end rebuild kit and come with everything.....It was the perfect bike for me and my 07 was super trick with RG3 diamond kit suspension, ill post some pics later tonight of them .....its the best of both worlds 250f handling with close to 450 power = perfection.
This is against 450's. This bike has heavy head work done .
I rode a 290 yamaha 250F and it had loads of low end. Felt like a 400cc. I didn't care so much for it though because it didn't hook up like a 250F and had no top end. It would great for old guys who just want to lug a small bike around.
They say the ticket is a big bore bike with the proper head mods to make it run stronger all through the rev range.
I had recorded lap times from my local track on both the 450 and 250 and I ended up being quite bit faster on the 250 simply because its not beating me up. So you might want to ride it for a bit stock and just see how the power is. Only downfall is the starts, get used to getting drug down the start by the 450's. I have some vids wear I clearly was first off the gate but about halfway I was getting passed lol.
The 250's are fun, you'll be manhandling it like a 125.......
We ran a regular Yoshi 250F pipe, Vortex ignition, and a well worked head and valve train. We also ran Carrillo rod with crank balanced to the bigger piston and Carrillo rod. The 50mm throttle body seemed to make a little more power on the big bore.
If you are not doing any head work, I would not do the big bore. Just bolting on the big bore kit does not really make the bike faster than a decent modified 250. If you do the head work and mapping the big bore is just insanely fast. The Vortex ignition really helped, we raised the rev limit to 13,800 and the bike would pull all the way to the limiter. With the set-up we ended up with, you could not get the bike rich enough with the stock ECU, with the Vortex you could.
I liked the Athena cylinder because it had larger water jackets and the largest piston. What we found however, is the Athena castings are often a little crude. We always machined the surfaces of the cylinder to ensure they were perfectly flat and would provide a good surface and the squish was right.
We also had instances where the dowel pin holes in the cylinder were not deep enough and could cause head gasket issues. If you decide on an Athena kit, make sure the dowel pin goes deep enough into the cylinder so that the head fully seats on the cylinder. (it is not obvious that the dowel pin is too long) You can simply mill the dowel to fix the problem.
The other big bore kits are based upon the OEM cylinder and boring them can result in more heat due to thinner than desired cylinder walls. That’s why they all use smaller pistons.
Pit Row
Also....you hit on a good point in which I was going to ask. Head work. I was thinking if I used an Athena kit ( or another brand ) , got a little head work done , maybe a hotrod cam and so forth......I could get something huilt that was faster than stock , but still be able to get some mileage out of the motor. I'd rather be a few ponies down on power if it gives me twice the life span of the motor.
BTW..using stock ignition as well?
This thread is turning out awesome! Cool listening to guys that have done what I was thinking all along.....and it's working!
Until now , I had no idea there were so many big bore making outfits out there. I knew there were a ton of motor mod guys....but actuall over bore CO.'s I didn't know about. Gives me some thinking to do.
I'll get another 250F sometime because they are so fun to ride and I'm faster on one except on really gnarly rutted and tacky tracks where the 450 helps carry you through the ruts with its brute power. Also, if you are in shape the 450 is one hell of a motocross weapon.
I second Slipdog on the 270....you will get more power and keep the over rev and not gain engine breaking.
If you're into trails and mountain riding the bigger bore is awesome!
BTW the fuel injected 250f feels like a big bore kit on a carbureted bike, even better.
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